1. Field of the Invention
This invention relates to a resin molding apparatus for producing molded articles of a resin material which have no runner nor gate portions thereon.
2. The Prior Art
Most of molded articles of a thermoplastic material produced by using metal molds are produced by using an injection molding technique, that is an injection molding apparatus. In the injection molding technique, a molding material which is heated into a fluidized (plasticized) state in a cylinder is injected under a high pressure into a cavity through a narrow runner or gate portion within a metal mold and is cooled into a rigid state or cured, and then the metal mold is opened and a molded article is taken out of the metal mold.
However, such an injection molding technique as described above has following drawbacks:
(1) since the material must run through a narrow flow path such as a runner or a gate, a very high injecting force is required, resulting in the necessity of a correspondingly high mold clamping force, and in order to attain such a high mold clamping force, the system must be large in size and hence the spacing for installation and the cost for equipment of the system will readily increase;
(2) since the injection molding apparatus essentially requires in its structure a runner, a gate and so on in order to produce a molder article therein and material remaining at such portions of the molded article after molding will be thrown away, the efficiency percentage is low; and
(3) where a change of arrangements such as color changing is effected frequently, a large amount of material remaining in a large injecting plunger will be thrown away, making a great loss.